1. Field of the Invention
The present invention relates to an optical amplifier capable of directly amplifying an optical signal in an optical communication system and its manufacturing method.
2. Description of the Related Art
As optical amplifiers, a prior art optical fiber amplifier and a prior art optical waveguide-type amplifier have been known (see: JP 4-46034 A and JP 4-213884 A). The prior art optical fiber amplifier and the prior art optical waveguide-type amplifier will be explained later in detail.
In the prior art optical fiber amplifier and the prior art optical waveguide-type amplifier, however, the intensity of an output light signal is small.